noun
Etymology: thionic International Scientific Vocabulary thion- (I) + -ic
1. : any of a series of unstable acids of the general formula H 2 S n O 6 in which the number of atoms of sulfur in the molecule varies from 2 to 6 — compare dithionic acid , polythionic acid
2.
[ thionic International Scientific Vocabulary thion- (II) + -ic ]
: a thio acid in which sulfur doubly bound to another atom (as in the thiocarbonyl group) is present — compare thiolic acid